This might not be such a big deal for some people, but it's always been a huge inconvenience with all current Canon DSLR cameras. The latest 1Dx camera from Canon showed that Video mode could be started from the same shutter button used to take photos. What does this mean? Well, this means that your most basic and most inexpensive wireless (not just infrared) shutter trigger systems will be able to start video mode.
The question I had was will the 5D Mark III have the same, and Mitch from Planet5D.com was able to get the information from Canon stating 'Yes, the basic shutter will start video mode'. There's also a constantly updated Blog article about all the main questions coming in about the 5D Mark III found here: http://blog.planet5d.com/2012/03/questions-answered-for-the-canon-eos-5d-mark-iii-hdmi-video/. [Thanks Mitch]
I'm not saying that's a reason to upgrade from a Canon 5D Mark II, but that was one very annoying feature Canon seems to have finally fixed. Guess what? That also means if you purchased a set of Yongnuo RF-602 or RF-603 triggers for your Speedlite flashes, those also can be used to start and stop video with your new Canon camera.
Some of you might already own a set, but ideally these very cheap Wireless trigger systems should now be able to start and stop video mode on all your 1Dx, Canon 5D Mark III, and hopefully all future Canon DSLRs.